1. Field of the Invention
The present invention is directed generally to wireless communication systems and, more specifically, to multiplexing control information in a physical channel transmitted in an uplink of a communication system.
2. Description of the Art
A communication system includes a DownLink (DL) that conveys signals from a Base Station (BS or NodeB) to User Equipments (UEs), and an UpLink (UL) that conveys signals from UEs to a NodeB. A UE, also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may be a wireless device, a cellular phone, a personal computer device, etc. A NodeB is generally a fixed station and may also be referred to as a Base Transceiver System (BTS), an access point, etc.
The UL carries data signals including information content, control signals providing information associated with the transmission of DL signals, and Reference Signals (RSs), which are commonly referred to as pilot signals. The DL also carries data signals, control signals, and RS.
A UL data signal provides data information and is conveyed through a respective Physical Uplink Shared CHannel (PUSCH). A UL control signal provides UL Control Information (UCI) and is conveyed through a respective Physical Uplink Control CHannel (PUCCH). However, when a UE has PUSCH transmission, it may convey UCI together with data information through the PUSCH.
A DL data signal provides data information and is conveyed through a respective Physical Downlink Shared CHannel (PDSCH). A DL control signal provides DL Control Information (DCI) and is conveyed by a respective DCI format transmitted through a respective Physical Downlink Control CHannel (PDCCH).
The UCI includes ACKnowledgment (ACK) information that is typically associated with a Hybrid Automatic Repeat reQuest (HARQ) process (HARQ-ACK). The HARQ-ACK information is usually transmitted by a UE in response to the reception of data Transport Blocks (TBs) conveyed via the PDSCH. Multiple HARQ-ACK information bits may be conveyed by a UE corresponding to positive acknowledgments (ACKs), negative acknowledgements (NACKs), or absence of reception, i.e., Discontinuous Transmission (DTX), in response to the correct, incorrect, or no reception of TBs, respectively, by the UE.
The UCI also includes Channel State Information (CSI), which may include Channel Quality Information (CQI), a Precoding Matrix Indicator (PMI), or a Rank Indicator (RI). The CQI provides the NodeB with a measure of the Signal to Interference and Noise Ratio (SINR) the UE experiences over sub-bands (Sub-band CQI) or over the whole (wideband CQI) DL operating BandWidth (BW). This measure is typically in the form of the highest Modulation and Coding Scheme (MCS) for which a predetermined BLock Error Rate (BLER) can be achieved for the transmission of TBs to the UE. The PMI/RI informs the NodeB how to combine the signal transmission to the UE from multiple NodeB antennas using the Multiple-Input Multiple-Output (MIMO) principle.
FIG. 1 is a diagram illustrating a conventional PUCCH subframe structure. Specifically, FIG. 1 illustrates a PUCCH transmission structure in a UL Transmission Time Interval (TTI), which for simplicity, is assumed to consist of one subframe.
Referring to FIG. 1, subframe 110 includes two slots 120. Each slot 120 includes NsymbUL symbols 130, where NsymbUL=7, used to transmit HARQ-ACK, CSI, or RS. The PUCCH transmission in the first slot is typically at a different BW part than the PUCCH transmission in the second slot in order to obtain frequency diversity. Some symbols in each slot may be used to transmit RS in order to provide channel estimation and enable coherent demodulation of the HARQ-ACK or CSI signal. The transmission BW includes frequency resource units, which are referred to as Physical Resource Blocks (PRBs). Each PRB includes NscRB sub-carriers, or Resource Elements (REs). Each PUCCH transmission is over one PRB 140. The last subframe symbol may be used to transmit a Sounding RS (SRS) 150, which provides the NodeB with an estimate of the UL SINR experienced by the UE.
FIG. 2 illustrates a conventional PUCCH structure in one subframe slot for HARQ-ACK signal transmission including 1 or 2 HARQ-ACK information bits.
Referring to FIG. 2, the HARQ-ACK bits 220 modulate a Constant Amplitude Zero Auto-Correlation (CAZAC) sequence 240 with Binary Phase Shift Keying (BPSK) for 1 HARQ-ACK information bit or with Quaternary Phase Shift Keying (QPSK) for 2 HARQ-ACK information bits, which is then transmitted after performing an Inverse Fast Fourier Transform (IFFT) operation. Each RS 250 is transmitted using a non-modulated CAZAC sequence.
For NscRB=12, CAZAC sequences of even length can be generated through a computer search for sequences satisfying the CAZAC properties. Different Cyclic Shifts (CSs) of a CAZAC sequence provide orthogonal CAZAC sequences as long as each CS value exceeds the channel propagation delay spread D (including time uncertainty errors). If Ts is the duration of a PUCCH symbol, the number of CSs resulting to orthogonal CAZAC sequences is equal to └Ts/J┘, where └ ┘ is the “floor” function that rounds a number to its immediately lower integer. Therefore, orthogonal multiplexing of RS and HARQ-ACK signal transmissions from different UEs can be achieved by allocating different CSs of a CAZAC sequence to different UEs in the same PRB for the transmissions of their RS and HARQ-ACK signals.
For a Frequency Division Duplex (FDD) system, a UE may transmit multi-bit HARQ-ACK information, e.g., when the UE receives multiple PDSCH in multiple cells over which it communicates with the NodeB. A PDSCH may convey more than one TB in accordance with the MIMO transmission principle. For a Time Division Duplex (TDD) system, a UE may additionally receive multiple PDSCH in respectively multiple DL subframes for which the UE transmits HARQ-ACK in one UL subframe.
The number of cells a UE is configured for PDSCH reception is denoted by C and the number of configured cells for which the UE is configured MIMO reception of 2 TBs in a PDSCH is denoted by C2, C2≦C. For an FDD system, the number of HARQ-ACK information bits a UE transmits in a PUCCH is fixed and equal to C+C2. For a TDD system, where HARQ-ACK for up to M PDSCH receptions in a cell is transmitted in one UL subframe, the number of HARQ-ACK information bits a UE transmits in a PUCCH is fixed and equal to M·(C+C2). If the number of HARQ-ACK information bits exceeds a predetermined value, a UE may apply HARQ-ACK spatial domain bundling and generate 1 HARQ-ACK information bit in response to each reception of two TBs in each respective PDSCH. With HARQ-ACK spatial domain bundling, a UE generates an ACK if it correctly receives both TBs of a PDSCH and generates a NACK otherwise. Then, the number of HARQ-ACK information bits is equal to C for a FDD system and equal to M·C for a TDD system.
FIG. 3 illustrates a conventional structure for multi-bit HARQ-ACK signal transmission in a first slot based on the Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing (DFT-S-OFDM) principle.
Referring to FIG. 3, after encoding and modulation using respectively, for example, a block code and QPSK (not shown for brevity), a set of the same HARQ-ACK bits 310 is multiplied with elements of an Orthogonal Cover Code (OCC) 330 and is subsequently DFT precoded 340. For example, for 5 symbols per slot carrying HARQ-ACK bits, the OCC has length 5 {OCC(0), OCC(1), OCC(2), OCC(3), OCC(4)} and can be either of {1, 1, 1, 1, 1}, or {1, exp(j2π/5), exp(j4π/5), exp(j6π/5), exp(j8π/5)}, or {1, exp(j4π/5), exp(j8π/5), exp(j2π/5), exp(j6π/5)}, or {1, exp(j6π/5), exp(j2π/5), exp(j8π/5), exp(j4π/5)}, or {1, exp(j8π/5), exp(j6π/5), exp(j4π/5), exp(j2π/5)}. The output is passed through an IFFT 350 and it is then mapped to a DFT-S-OFDM symbol 360. As the previous operations are linear, their relative order may be inter-changed. Because the signal transmission is in 1 PRB of NscRB=12 REs, there are 24 encoded HARQ-ACK bits transmitted in each slot with QPSK (12 HARQ-ACK QPSK symbols). The same or different HARQ-ACK bits may be transmitted in the second slot of the subframe. In addition to HARQ-ACK signals, RSs are transmitted in each slot to enable coherent demodulation of the HARQ-ACK signals. The RS is constructed from a length-12 CAZAC sequence 370, which is passed through an IFFT 380 and mapped to another DFT-S-OFDM symbol 390.
FIG. 4 illustrates a conventional UE transmitter block diagram for HARQ-ACK signals.
Referring to FIG. 4, the HARQ-ACK information bits 405 are encoded and modulated by an encoder and modulator 410 and then multiplied with an element of the OCC 425 for the respective DFT-S-OFDM symbol by multiplier 420. The output of the multiplier 420 is then precoded by DFT precoder 430. After DFT precoding, sub-carrier mapping is performed by sub-carrier mapper 440, under control of controller 450. Thereafter, the IFFT is performed by IFFT 460, a Cyclic Prefix (CP) is added by CP inserter 470, and the signal is filtered by filter 480 for time windowing, thereby generating the transmitted signal 490. For brevity, additional transmitter circuitry such as digital-to-analog converter, analog filters, amplifiers, and transmitter antennas are not illustrated in FIG. 4.
FIG. 5 illustrates a conventional NodeB receiver block diagram for HARQ-ACK signals.
Referring to FIG. 5, after receiving a Radio-Frequency (RF) analog signal and converting the analog signal to a digital signal 510, the digital signal 510 is filtered by filter 520 for time windowing and a CP is removed by CP remover 530. Subsequently, the NodeB receiver applies a Fast Fourier Transform (FFT) by FFT 540, performs sub-carrier demapping by sub-carrier demapper 550 under the control of controller 555, and applies an Inverse DFT (IDFT) by IDFT 560. The output of the IDFT 560 is then multiplied with an OCC element 575 for the respective DFT-S-OFDM symbol by multiplier 570. An adder 580 sums the outputs for the DFT-S-OFDM symbols conveying HARQ-ACK signals over each slot, and a demodulator and decoder 590 demodulates and decodes the summed HARQ-ACK signals over both subframe slots to obtain the transmitted HARQ-ACK information bits 595.
FIG. 6 illustrates a conventional structure for CSI signal transmission in a PUCCH subframe slot that includes CSI signals and RSs for enabling coherent demodulation of the CSI signals.
Referring to FIG. 6, after encoding, for example, using a block code, and modulation, for example, using QPSK (not shown for brevity), the CSI bits 610 modulate a CAZAC sequence 630, which is then transmitted after performing the IFFT operation as it is subsequently described. Each RS 640 is transmitted through the non-modulated CAZAC sequence.
FIG. 7 is a block diagram illustrating a UE transmitter structure for a CAZAC sequence. Specifically, FIG. 7 illustrates a UE transmitter structure for a CAZAC sequence 710 that can be used without modulation as an RS or with modulation as a CSI signal.
Referring to FIG. 7, the REs corresponding to the assigned PUCCH PRB are selected for mapping the CAZAC sequence 710 by sub-carrier mapper 730 under control of controller 720. IFFT is then performed by IFFT 740, and a cyclic shifter 750 applies a CS to the output of the IFFT 740. A CP inserter 760 adds a CP to the signal and the filter 770 for time windowing filters the signal, thereby generating transmitted signal 780.
FIG. 8 is a block diagram illustrating a NodeB receiver structure for a CAZAC sequence. Specifically, FIG. 8 illustrates a NodeB receiver block diagram for CSI signals that are transmitted using a modulated CAZAC sequence.
Referring to FIG. 8, an RF analog signal is received and converted into a digital received signal 810, which is filtered by filter 820 for time windowing. Thereafter, the CP is removed by CP remover 830. Subsequently, the CS is restored by cyclic shifter 840, and a FFT is applied by FFT 850. A sub-carrier demapper 860 selects transmitted REs, under control of controller 865. and the selected REs are then correlated with a replica 880 of the CAZAC sequence by multiplier 870, thereby generating output 890, which can then be passed to a channel estimation unit, such as a time-frequency interpolator, in case of a RS, or to detect the transmitted information, in case the CAZAC sequence is modulated by the CSI bits.
Although the PUCCH structures for transmission of HARQ-ACK or CSI signals were illustrated for the first subframe slot, they are respectively the same in the second subframe slot. An exception occurs in subframes, if any, supporting SRS transmission, where the last DFT-S-OFDM symbol in the second slot may be punctured as illustrated in FIG. 1. The PUCCH resource (PRB, CS) for CSI signal transmission is explicitly informed to the UE by the NodeB, while the PUCCH resource (PRB, CS, OCC) for the HARQ-ACK signal transmission may be either explicitly or implicitly informed.
If a UE is to transmit HARQ-ACK information and CSI in the PUCCH during the same subframe, the ability to do so depends on the number of HARQ-ACK bits. In case of 1 or 2 HARQ-ACK bits, the PUCCH structure for CSI transmission in FIG. 6 can be used and the HARQ-ACK bits can be conveyed by modulating the RS with an OCC that depends on the value of the HARQ-ACK bits.
Alternatively, the HARQ-ACK bits may be jointly encoded with the CSI bits.
However, these mechanisms are not feasible or practical in case of multiple HARQ-ACK bits.
For example, joint encoding of multiple HARQ-ACK bits and CSI bits may be problematic due to the different respective reliability requirements and due to the resulting worse detection reliability for both as the effective coding rate increases.
An alternative is for the UE to separately transmit in the same subframe HARQ-ACK signals and CSI signals. However, this is also associated with several drawbacks including an increase in the Cubic Metric (CM) of both transmissions and the need to apply Maximum Power Reduction (MPR) to satisfy spectral emission requirements. These shortcomings effectively prohibit the transmission of multiple HARQ-ACK bits and CSI bits in the PUCCH in the same subframe. Then, as HARQ-ACK is more important, CSI is not transmitted whenever it coincides with the transmission of multiple HARQ-ACK bits.
The HARQ-ACK multiplexing capacity per PUCCH PRB using the DFT-S-OFDM transmission structure is typically determined by the length of the OCC applied in the time domain, which in FIG. 3, is equal to 5, as the RS multiplexing capacity is determined by the number of CS providing orthogonal CAZAC sequences, which is typically larger than 5. If the last DFT-S-OFDM symbol in the second slot (for the structure illustrated in FIG. 3) is punctured in order to support SRS transmission, the HARQ-ACK multiplexing capacity is reduced from 5 to 4, as there will be 4 DFT-S-OFDM symbols available for HARQ-ACK signal transmission in the second slot and this determines the overall multiplexing capacity.
Therefore, there is a need to enable transmission of HARQ-ACK signals and CSI signals by a UE in the PUCCH during the same subframe, while avoiding the shortcomings associated with the conventional transmission method.
There is another need to determine conditions for the joint or separate coding and transmission of HARQ-ACK information bits and CSI information bits from a UE.
Finally, there is another need to maximize UE multiplexing capacity per PUCCH PRB for HARQ-ACK signal transmission, while also enabling SRS transmission by a UE.